Windshield wiper system

ABSTRACT

A dual motor windshield wiper system and windshield washer system integrated together into a single assembly. The system includes two motors (22, 22&#39;), a control circuit (12), a fluid reservoir (120), a pump (112), and at least one mounting member (108, 108&#39;) that supports said motors. The reservoir can be located between the two motors and can be supported in place by the motors. The motors can be thermally coupled to the reservoir so that fluid within the reservoir acts as a heat sink for the motors. The positions of the wipers can be controlled to follow targeted positions that are determined in accordance with acceleration, velocity, and deceleration values that are calculated using a wiper speed setting selected by the vehicle driver.

This Application claims Beneficial of Provisional application Ser. No.60/034,269 filed Jan. 3, 1997.

This application claims benefit of Provisional Application No.60/034,217, filed Jan. 3, 1997, and entitled “WINDSHIELD WIPER SYSTEM”.

TECHNICAL FIELD

The present invention relates generally to windshield wiper systems and,more particularly, to automotive windshield wiper system that utilizeindividual brushless dc motors for coordinated, but mechanicallyindependent control of the windshield wipers.

BACKGROUND OF THE INVENTION

Automotive windshield wiper systems typically use a pair of motor drivenwiper blades to clean the windshield. In most systems, a single motor isused with a mechanical linkage between the wiper blades so that thesingle motor provides simultaneous, synchronous reciprocation of the twowiper blades. Automotive vehicles also typically include a windshieldwasher system that sprays washer fluid onto the windshield to aid in thecleaning of the windshield by the wipers. The washer system can includea washer fluid reservoir to store the washer fluid, a pair of nozzles tospray the fluid onto the windshield, and a pump to supply the washerfluid to the nozzles. While these washer systems are commonly located inthe engine compartment near the windshield wiper system itself,integration of the washer system and the windshield wiper system into acompact assembly can be difficult because of the moving mechanicallinkages used to drive both wipers from a single motor.

Windshield wiper systems have been designed that utilize separateelectric motors for each of the wipers. See, e.g., U.S. Pat. No.4,585,980 to Gille et al., U.S. Pat. No. 4,665,488 to Graham et al.,U.S. Pat. No. 4,900,995 To Wainwright, and U.S. Pat. No. 5,252,897 toPorter et al. While eliminating the mechanical linkage between thewipers, these dual motor system have at times been disfavored becauseoperation of the two motors must be properly coordinated to preventcollisions between the two wipers. Coordination of the motors has beenaccomplished using position feedback by sensing, for example, theposition of each motor's armature or by using position sensors on thewiper levels or the windshield itself, as in U.S. Pat. No. 5,157, 314 toKühbauch.

In the field of motor controllers generally, motor position feedback hasbeen used in brushless dc motors for commutation of the motor windings.This has sometimes been done using Hall Effect sensors, as in U.S. Pat.No. 4,680,515 to Crook, U.S. Pat. No. 4,723,100 to Horikawa et al., andU.S. Pat. No. 4,897,583 to Rees. The output of these Hall Effect sensorshave also been used along with a clock oscillator to produce positionand tachometer signals for operational control of the motor. See, forexample, U.S. Pat. No. 4,415,844 to Mendenhall et al. and U.S. Pat. No.4,717,864 to Fultz.

While suitable for use in windshield wiper systems, the use of theabove-noted brushless dc motor controllers in a windshield wiper systemthat uses separate position sensors for coordination of the wipers canresult in an unnecessarily complicated design.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a dual motorwindshield wiper system that includes a windshield washing system allintegrated into a single drop-in assembly. The assembly can include bothwiper motors, a windshield washer fluid reservoir, a washer fluid pump,and at least one mounting member that supports the motors, fluidreservoir, and pump and that is adapted to attach the assembly to thevehicle.

In accordance with another aspect of the invention, the fluid reservoircan be located between the motors in the area that is typically used forthe mechanical linkages required for a single motor system. The motorscan be attached to separate mounting members and together can supportthe fluid reservoir between them. Alternatively, the reservoir can beattached to the one ore more mounting members and can provide thenecessary support for the motors. The reservoir can have recesses in itsouter surface that can be used as the motors' housings. The motors canbe thermally coupled to the interior of the reservoir so that washerfluid within the reservoir operates as a heat sink to remove heat fromthe motors. Similarly, one or more power devices used by the windshieldwiper system's control circuit can be thermally coupled to the interiorof the reservoir to sink heat produced by the devices during use.

In accordance with another aspect of the invention, there is provided adual motor windshield wiper system in which encoders are used to providepulses indicative of angular displacements of the motors, with thepulses being used not only for commutation of the motors, but also fortracking the position of the wipers. This reduces the complexity of thecontrol circuitry by using a single encoder for both commutation andposition tracking.

In accordance with another aspect of the invention, the windshield wipersystem includes a control circuit that is operable to automaticallydetermine a park or home positions without the use of limit switches.This can be accomplished by rotating the wipers towards their homeposition until further rotation is obstructed by the cowl cover or someother part of the vehicle. The wipers can then be rotated upward by asmall amount with current position of the wipers then being used asreference for determining the absolute position of the wipers duringnormal operation.

In accordance with another aspect of the invention, the control circuitcan provide control of each wiper's position by comparing the actualposition to target position values that are generated usingacceleration, velocity, and deceleration values determined in accordancewith the wiper speed selected by the vehicle operator.

In accordance with another aspect of the invention, the control circuitis operable to measure the current used by the motors and, using themeasured current, is operable to determine an environmental condition ofthe windshield (e.g., wet, dry, icy). Outside air temperature and othersensed parameters can also be used along with motor current to determinethe environmental condition of the windshield.

In accordance with yet another aspect of the invention, there isprovided a windshield washer system having a control circuit operable tocontrol the spray of washer fluid onto the windshield in accordance withat least one measured parameter. This parameter can be, for example,vehicle speed, so that overspray of the washer fluid can be avoided athigher speeds.

In accordance with another aspect of the invention, there is provided awindshield wiper system which includes a user-selectable intermittentmode of operation, wherein the control circuit is operable pause themotors each time the wipers reach either of their ends of their travel.For a windshield wiper system in which the wipers sweep up from thebottom center of the windshield to opposite sides of the windshield,this system is advantageous since the wipers do not obscure the driver'sview in either their inboard or outboard position and can therefore bepaused at each end of travel rather than only at the end of a completecycle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a preferred embodiment of an electroniccontrol circuit for a windshield wiper system of the present invention;

FIG. 1A is a block diagram of another preferred embodiment of anelectronic control circuit;

FIG. 2 is a flow chart depicting the operation of the windshield wipersystem of FIG. 1;

FIG. 3 is a flow chart depicting a selected portion of the flow chart ofFIG. 2 in greater detail;

FIG. 4 is a graph showing the velocity of a wiper blade as a function oftime and is provided for the purpose of deriving the velocity,acceleration, and deceleration values utilized in the system operationof FIGS. 2 and 3;

FIG. 5 depicts velocity curves representing the velocity of each of twowipers of the windshield wiper system of FIG. 1;

FIG. 6 depicts position curves representing the positions of the twowipers resulting from their operation according to the velocity curvesof FIG. 5;

FIG. 7 is a side view of one embodiment of a mechanical assembly for awindshield wiper system of the present invention;

FIG. 8 is a top view of the mechanical assembly of FIG. 7.;

FIG. 9 is a side view of another embodiment of a mechanical assemblyshowing an integral washer fluid reservoir and motor housing; and

FIG. 10 is a side view of another embodiment of a mechanical assemblyshowing a heat sink that forms one wall of the washer fluid reservoir.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the illustrated embodiment is separatedinto two sections, the first being directed to the electrical andcontrol aspects of the illustrated embodiment and the second beingdirected to the mechanical and assembly aspects of the illustratedembodiment.

WINDSHIELD WIPER ELECTRONIC CONTROL SYSTEM

As shown in FIG. 1, an electronic control system designated generally as10 includes a system controller 12 that drives a pair of electric motors14, 14′. Controller 12 operates motors 14, 14′ in accordance withvarious commanded inputs, operational parameters, and environmentalconditions. The commanded inputs include one or more user inputs 16 suchas a windshield wiper switch that is used by the vehicle driver toactivate the windshield wipers and to set the speed and, in the case ofinterval wipers, to specify the intermittent mode and the delay betweenwiping cycles. Operational parameters include the torque and position ofeach of the motors, and can also include vehicle speed obtained from adigital tachometer of other vehicle speed sensor 18. As discussed ingreater detail below, these parameters are used by controller 12 forvarious purposes, including determination and adjustment of the positionof the wiper blades, overcurrent protection for the motors, anddetermination of the condition of the windshield (e.g., dry, wet,ice-covered). Environmental conditions include air temperature which canbe obtained via a thermistor or other conventional air temperaturesensor 20. As will also be discussed below, the measured air temperaturecan be used along with the motor torque and vehicle speed to determinethe condition of the windshield.

Motors 14 and 14′ each include a brushless dc motor 22, 22′, a drivemodule 24, 24′, and a gear box 26, 26′, respectively, DC motors 22 and22′ each include respective encoders 28, 28′ that are used by drivemodules 24, 24′ to provide electronic commutation of the motor windingsin a conventional manner. Gear boxes 26 and 26′ have respective outputshafts 30, 30′ that are connected directly to their associated wiperblades (not shown). The construction and operation of motors 14 and 14′are the same—only their commanded movements are different. Therefore,except where otherwise indicated, the following discussion will bedirected only to motor 14 and its use in connection with controller 12and it will be understood that the discussion applies equally to motor14′.

Drive module 24 receives commands from controller 12 in the form ofdifferential drive COMMAND+ and COMMAND-signals and operates motor 22 inthe commanded direction and at the commanded speed. Drive module 24provides controller 12 with feedback information that is used bycontroller 12 in various ways, including control of the wiper bladeposition and monitoring for an overcurrent condition. This feedbackinformation includes a tachometer signal and a torque signal. A signalground is also provided as a reference for the tachometer and torquesignals.

The tachometer signal is a pulse train having a pulse repetition rate,or frequency, that is indicative of the motor speed. This signal isgenerated by drive module 24 using the position signals that encoder 28provides for use in commutation of the motor windings. In theillustrated embodiment, encoder 28 utilized three Hall effect sensors toprovide the position pulses. Controller 12 uses this tachometer signalto track the position of the wiper blades. More specifically, since eachsuccessive pulse of the tachometer signal represents a particularangular displacement, the position of the wiper blade can be determinedas a function of the number of pulses that have occurred since the wiperblade has moved from one of its ends of travel. This permits controller12 to know the instantaneous position of the wiper blades at any time.In the illustrated embodiment, encoder 28 utilizes three Hall effectsensors to provide the position pulses that are used to generate thetachometer signal. As will be appreciated by those skilled in the art,optical and other types of encoders could be used instead of Hall effectsensors to provide the signals used for both commutation of the motorwinding and tracking of the blade position.

The torque signal is actually a measure of the motor current that can beconverted to a torque value by controller 12. As is known, measurementof the motor current can be accomplished using a current sensor inseries with the motor's ground connection. The current sensor can be asmall valued wirewound resistor or other resistance having a smalltemperature coefficient. The motor current is converted to a torquevalue using the torque constant associated with motor 14. The torqueconstant is stored within the memory of controller 12 and accessed asneeded. The resulting torque signal is used to protect motor 22 againstan overcurrent condition and is used in conjunction with other inputs todetermine the condition of the windshield.

Another embodiment of the electronic control circuit is shown in FIG.1A. In this figure, all of the components except system controller 32are the same as that shown in the embodiment of FIG. 1 and thereforehave been labelled used double primes (″) where unprimed numerals wereused in FIG. 1 and using tripe primes (″′) where primed numberals wereused. The embodiment of FIG. 1A differs from that of FIG. 1 in that thefunctionality of drive modules 24 and 24′ of FIG. 1 have beenincorporated into controller 32. Thus, the three Hall effect sensoroutputs from each of the encoders are provided to controller 32 andcontroller 32 generates the necessary phased drive signals for the motorwindings of each motor.

Turning now to FIG. 2, the method utilized by controller 12 to operatemotors 14 and 14′ will now be described. In the following description,reference numerals enclosed within angled brackets <> denote thenumbered steps within the figures. Upon start-up <40>, controller 12performs any needed setup tasks, such as configuring the hardware (e.g.,setup of the controllers's I/O ports) and initializing the variablesused by controller 12. Then, a check is made <42> to determine if theuser has activated the wipers via the windshield wiper switch 16.

If the windshield wipers have not been activated, then the controllerchecks the current position of the wipers to determine if they arelocated at the “park” position <44>. The park position is the locationat which the wipers are stored when the windshield wiper system is notactivated. If desired, the part position can be the same as the “home”position which is one of the end points of travel of the wiper bladeduring a normal operating cycle. As mentioned above, the position ofeach wiper blade is tracked using the tachometer signal pulses. Morespecifically, a register or counter variable for each wiper can beinitialized to zero when the wipers are in their part position. Then,for each wiper, the counter is incremented by one for each tachometersignal pulse occurring as a result of the motor being operated in one(e.g., clockwise) direction and is decremented by one for each pulseoccurring as a result of the motor being operated in the other (e.g.,counter-clockwise) direction. In the illustrated embodiment, thistracking is provided by controller 12. If the wipers are both in theirpark positions <44>, then the process loops back to block <42 > and thisloop repeats until the user activates the windshield wipers vis userinput 16. If, at block <44>, one or both of the wipers are not in theirrespective park positions, then a part routine <46> is run that movesboth wipers to their park positions. Thereafter, the process returns toblock <42> to again for user-activation of the wiper system.

If, at block <42>, the user has switched on the windshield wipers, thencontroller 12 begins a normal wiping cycle. The first step in this cycleis to determine the current positions of the wiper blades <48>; forexample, by checking the current value of the tachometer pulse counters.Then, the wiping mode, system status, and user-selected speed are read<50>. The wiping mode is specified by the user and indicates whether thewipers are to operate in the intermittent or continuous mode. As will beappreciated, other wiping modes are possible and the system is notlimited to the types of synchronized movement provided by mechanicallylinked systems. For example, in another mode, the wiper speeds mayautomatically change from a user-selected setting based upon any of thesensed vehicle operating and/or environmental parameters. The systemstatus information is used by controller 12 to verify that the controlsystem is ready to operate motors 14, 14′. The status information caninclude any desired relevant information to indicate, for example, thatthe motor windings are not somehow shorted or that operating power forthe motor is present. The user-selected speed specifies how quickly thewipers are to move through their range of travel. As with the wipingmode, the selected speed can be inputted by a user via input device 16.

Once the user-selected speed has been obtained, acceleration (acc),velocity (v), and deceleration (dec) values can be determined <52> foreach motor using equations [5]-[7] that are discussed farther below inconnection with FIG. 4. These values are used by controller 12 todetermine the target positions and predicted torque values at discretepoints in time during the wiping cycle <54>. These position and torquevalues can be stored in arrays and accessed as needed for comparison toactual positions and torques.

The next step <56> is to activate motors 14 and 14′ to begin wipermovement using a position servo loop that operates to minimize the errorbetween the actual and target values of the wiper position. Once themotors are energized, the tachometer signal is examined to determinewhether either of the motors are moving <58>. If so, the currentposition is read <60> and compared to the appropriate target positionfrom the position array to determine the position error. The positionerror is then checked <61> to determine if it exceeds a preselectedlimit. If neither of the wipers are too far out of position, then acheck is made to determine if the wipers are at the home position <62>.If either wiper is out of position, then a reset routine is performed<62> prior to moving to block <63>. The reset routine involves stoppingboth motors, then activating one to move its associated wiper blade toits end of travel and then activating the other motor to move itsassociated wiper blade to its end of travel (i.e., at the end of awiping cycle). If at block <63> the wipers are not in the home position,the process loops back to perform another iteration of the main loop,starting with reading of the mode, system status, and user-selectedspeed settings. Once the wipers reach the home position <63>, a check ismade to determine if the wipers have been set to the intermittent mode<64>. If not, the process returns to block <42> to check whether thewipers have remained activated or have been turned off. If the wipershave been set to the intermittent mode, then the dwell time selected bythe user is read <66> and the wipers are then paused <68> for acorresponding amount of time. The process then returns to block <42>.

If, a block <58>, neither of the motors are moving, then an errorcondition is assumed and the values of current and position error ofboth of the motors are read <70>. If the magnitude of the motor currentis greater than a preset limit <72>, then a reset routine is performed<74>. This reset routine is the same as that performed at block <62>,except that after the routine is finished, the process returns to block<42> to restart its normal wiping cycle. If, at block <72>, the motorcurrent was within the predefined limits, then the magnitude of theposition error is checked to determine if it is above a predefined limit<76>. If not, the process returns to block <58> and will loop throughblocks <70>, <72>, and <76> until at least one of the motors startsmoving or the motor current or position error exceeds their respectivelimits. If, at block <76>, the position error exceeds its limit, thenthe reset routine is run <74>.

By utilizing the reset routine whenever the position error exceeds apredefined limit, the system can avoid collisions between the wipersthat might otherwise occur if one or both wipers become too far out of adesired position. Similarly, by utilizing the reset routine whenever themotor current error exceeds a predefined limit, the system can preventan overcurrent condition that could otherwise damage either the motorsor some other electrical or mechanical component of the system.

The process of blocks <70-76> that check for position and torque errorare shown more fully in FIG. 3. As discussed above, the target positionsof the wiper blades at each of a number of time intervals spanning asingle cycle can be stored in an array. Predicted torque valuescorresponding to each time interval could also be stored as an array.The sizes of these arrays are fixed and the length of the time intervalsdepends upon the user-selected cycle time (e.g., fast or slow wiperspeed). As will be appreciated, by tracking the amount of elapsed timesince the beginning of a cycle, the current interval can be determinedat any time using the known total cycle time and known number ofintervals. Once the current interval is determined, the expectedposition and torque can simply be looked up within their respectivearrays.

Thus, the first step in checking the position and motor current error isto determine how much time has elapsed since the beginning of thecurrent wiping cycle <80>. Then, the actual motor positions are read<82 >, as well as the motor currents <84>. The motor current is thenconverted into a torque value <86> using the torque constant for themotor. Based on the elapsed time, the current time interval isdetermined and the position and torque arrays are accessed <88, 90> todetermine the target position and predicted torque values. The positionerror is then calculated <92> based upon the difference between theactual and target positions. Similarly, the torque error is calculated<94> based upon the difference between the actual and predicted torquevalues. For each motor, these errors are compared to preselected limits<96, 98 > and the reset routine is run <74 > if either error is beyondthe prescribed limits. Otherwise, the process returns to block <58> ofFIG. 2.

Controller 12 and drive module 24 together provide the position servoloop, with controller 12 generating the COMMAND signal based upon thedifference between the measured position and a target position. Asdiscussed above, the tachometer signal feedback is used to determine thecurrent position of the wiper. The target position is determined usingthe predetermined acceleration, velocity, and deceleration valuescalculated at block 52 of FIG. 2. Referring now to FIG. 4, thederivation and use of those equations will now be discussed. As shown inthat figure, one half of a single wiper cycle involves an initial period0<t<t₁ of constant acceleration from rest, followed by a constantvelocity period t₁<t<t₂, followed by a final period t₂<t<T of constantdeceleration back to rest. Given that the wiper must traverse a distanceD in an amount of time T, the value of the maximum velocity v and thetransition points t₁ and t₂ are selected so as to minimize theacceleration and deceleration values while still covering the distance Din the allotted time T and while maintaining the desired positionalsynchronism between the two wiper blades. Although FIG. 4 depicts onlyone half of a full wiper cycle, it will be appreciated that the returnhalf of the cycle can simply be the reverse of the first half (i.e.,acc_(r)=dec_(f), dec_(r)=acc_(f), and v_(r)=v_(f), where subscript findicates the forward rotation used during the first half of the cycleand subscript r indicates the reverse rotation used during the secondhalf of the cycle).

The derivation of the equations used for calculating the acceleration,velocity, and deceleration values will now be described in connectionwith FIG. 4 for a single wiper. The distance covered during accelerationis defined by the equation: $\begin{matrix}{D_{1} = {\left( \frac{v}{2} \right){\left( t_{1} \right).}}} & \text{[1]}\end{matrix}$

The distance covered during constant velocity is defined by theequation: $\begin{matrix}{D_{2} = {(v){\left( {t_{2} - t_{1}} \right).}}} & \text{[2]}\end{matrix}$

The distance covered during deceleration is defined by the equation:$\begin{matrix}{D_{3} = {\left( \frac{v}{2} \right)\left( {T - t_{2}} \right)}} & \text{[3]}\end{matrix}$

Therefore,

D=D ₁ +D ₂ +D ₃  [4]

Substituting equations [1], [2], and [3] into equation [4] and solvingfor the velocity v yields: $\begin{matrix}{v = \frac{2D}{T\left( {1 - a + b} \right)}} & \text{[5]}\end{matrix}$

where t₁=aT and t₂=bT.

The acceleration during the first interval equals the slope of the linein that interval. Therefore, ${{acc} = \frac{v}{t_{1}}},$

which by substituting in equation [5] for the velocity yields:$\begin{matrix}{{acc} = \frac{2D}{\left( T^{2} \right)(a)\left( {1 - a + b} \right)}} & \text{[6]}\end{matrix}$

Similarly, the deceleration during the last interval can be calculatedas follows: $\begin{matrix}{{dec} = \frac{2D}{\left( T^{2} \right)\left( {1 - b} \right)\left( {1 - a + b} \right)}} & \text{[7]}\end{matrix}$

As will be understood by inspection of FIG. 4, the instantaneous targetposition at any point t in time is equal to the area under the curveover the interval 0 to t and can be determined using one or more of theacceleration, velocity, and deceleration values. As indicated byequations [5], [6], and [7], the acceleration, velocity, anddeceleration values can be determined as a function of parameters a andb (i.e., as a function of the transition points t₁ and t₂).

The velocity curve and equations shown in FIG. 4 are for only one of thetwo wiper blades. It will be appreciated that the same equations can beused for the other wiper blade, and that for coordinated movement, thetraversal time T will remain the same while the distance D to be coveredmay be different. Also, the values of parameters a and b that define theacceleration transition points may be different. For a two wiper system,the parameters a and b for each of the two wipers can be determinedempirically as follows. First, the ranges of travel for each of the twowiper blades is separated into a number of intervals (e.g., ten), eachof which corresponds to an incremental point in time during half of thewiping cycle. The wipers are then both manually set at the respectivepositions that they would desirably occupy after the first interval oftime (e.g., at time T/10) and these positions are recorded. As mentionedabove, these positions are represented by counters that are incremented(or decremented depending upon the direction of rotation) using thetachometer signal. Then, the two wiper blades are moved to the positionsthat they would desirably occupy after the second interval of time.These positions are saved in the next position of its associated arrayand the process is repeated for each of the remaining intervals. Usingthese desired positions, the values of a and b for each of the wipersare then determined either by trail and error or by a suitablecurve-fitting algorithm. In selecting values for a and b, it ispreferable to minimize the acceleration and deceleration levels as muchas possible within the constraints of maintaining the requiredpositional coordination between the two wipers.

FIG. 5 provides an exemplary set of velocity curves for each of twowipers in a wiper system designed to rotate the two wipers in oppositedirections. The wipers initially start at a lower, central portion ofthe windshield and are rotated up and away from each other towards theopposite sides of the windshield. As will be appreciated, the values ofa₁ and b₁ for the first wiper and a₂ and b₂ for the second wiper areselected so that the first wiper accelerates faster than the second, butfor a shorter amount of time. Since the wipers are positioned relativelyclose to each other when in the park and home positions, thisdifferential in acceleration results in the first wiper moving up andaway from the park and home positions faster than the second wiper,thereby helping to avoid any contact between the two.

FIG. 6 shows the position of the two wiper blades as a function of time,using the velocity curves of FIG. 5. FIG. 6 illustrates the growingseparation of the two wiper blades resulting from the differingaccelerations of the wipers from their park positions. FIG. 6 alsoillustrates the manner in which the values of a and b can be determinedfor each wiper. The desired positions of the wiper blades at eachinterval can be plotted and the values of a and b determined byinspection of the resulting plot.

Once the values of parameters a and b have been determined for each ofthe wipers, controller 12 is programmed with these values and canthereafter generate the acceleration, deceleration, and velocity valuesusing the user-selected speed setting. Thereafter, controller 12 canthan generate the array of target positions at each desired intervalover the course of the wiping cycle.

As will be appreciated, the position of the wiper blades is controlledby regulating the motor current so as to keep the wiper blades at thetarget positions. The motor current, or torque, is also used as feedbackinformation for other purposes, including: 1) over-current protection asdiscussed above; (2) determination of a reference position (e.g., parposition) without the need for limit switches; and (3) determination ofwindshield conditions.

Automatic determination of a desired park position for the wiper bladescan be accomplished as follows. First, the wipers are driven towards andthen through the park position until they come into contact at the baseof the windshield with a positive stop (such as the cowl cover) thatacts as a known reference. This positive stop prevents further rotationof the wipers, thereby causing the motor current to rise relativelysharply. This condition is determined by examining torque signal and itsfirst derivative so that it can be distinguished from torque changes dueto other obstructions or due to the state of the windshield. When thiscondition is sensed, the current position of the wiper can be used as areference for determining the absolute position of the wiper. The wipercan then be rotated away from the cowl cover by a small, preselectedamount and this new position taken as the part position. The amount ofrotation to the home position (if different from the part position) andto the other end of travel can be predetermined by testing and willdepend upon such factors as the shape of the windshield glass, thelength of the wiper blades, and the location of the wiper arms' centersof motion. Thus, the end positions and range of travel of the wiperblades can be set (and reset) without the need for limit switches orslip rings. Thus, fewer parts are required resulting in a decrease inthe number of possible failure modes. This method of determining adesired park position can be carried out during vehicle assembly by theautomobile manufacturer or could be programmed to occur in response to apreselected event, such as the ignition being switched on or a certainnumber of windshield wiper activations having occurred. Also, it will beappreciated that this same method of determining a desired park positioncan be utilized for many different windshields with only a minorsoftware change.

The amount of torque supplied by the motors to move the wiper bladesacross the windshield depends upon the condition of the windshield. Forexample, more torque is required to operate the wipers when thewindshield is dry than when it is wet. Thus, motor torque can be used inconjunction with the outside and/or inside air temperature, vehiclespeed and, if desired, other operational parameters to determine thecondition of the windshield. Once the condition of the windshield hasbeen determined, the windshield wiper system, windshield washing system,and/or the vehicle's climate control system can be automaticallyactivated as needed to clean the windshield. Also, the acceleration,deceleration, and velocity values can be calculated and/or updated asdesired to accommodate different environmental circumstances. Rainsensors and other such additional sensors can be used in lieu of or inaddition to the motor torque to provide controller 12 with dataindicative of the condition of the windshield.

The position information provided by the tachometer signal can also beused for purposes other than controlling the wiper position. Forexample, activation of the wiper fluid spray can be coordinated with thewiper blade position. Thus, a single momentary push by the vehicleoperator on a windshield washer switch could result in automatic timingof the washer switch could result in automatic timing of the washerspray to insure that fluid is applied to the windshield prior to wipingin both directions.

The software control of the wiper blades also provides the windshieldwiper system with additional capabilities. For example, a count of thetotal number of wiping cycles can be maintained and this informationused to predict wiper blade failure. A signal can be provided to theoperator as a warning of an impending blade failure. Also, the wiperscan be paused at each end of travel when in the intermittent mode,rather than only when in their home positions. This could be implementedsimply by changing block <62> of FIG. 2 so that it checks whether thewiper blade is at either end of travel. This type of intermittentoperation can be advantageous in light rain or mist situations where asingle wipe across the windshield is sufficient to remove theobstruction and where an immediate return wipe across the dry windshieldwould result in smearing and/or noise. Also, this additional pausereduces the average current draw of the system.

Windshield Wiper Mechanical Assembly

The use of separate dc motors to provide independent control of thewiper blades eliminates the necessity of mechanical linkages between thetwo wiper blades. The illustrated windshield wiper mechanical assemblyof the invention takes advantage of the available room between the twomotors by providing an integrated windshield wiper system that includesnot only the motors and associated circuitry, but also the washer fluidreservoir, pump, nozzles, and, if desired, the exterior trim cowl cover.These components are all connected together as a single, drop-inassembly that significantly reduces the amount of labor required toinstall the assembly within the vehicle.

Turning now to FIG. 7, a first embodiment of the mechanical assembly ofthe invention is shown and is designated generally as 100. The assemblyincludes a pair of motors 102, 102′ that drive respective right anglegear boxes 104, 104′ having output shafts 106, 106′, respectively. Gearboxes 104, 104′ are each attached to a respective mounting bracket 108,108′ that is used to secure assembly 100 to the vehicle. The assemblyalso includes a fluid reservoir 110 that is supported at each end bymotors 102 and 102′. Reservoir 110 can be an injection molded componenthaving unitary fingers at each end that define a recess into which themotor housings extend. In this way, reservoir 110 is supported andconstrained from movement by motors 102 and 102′. The assembly furtherincludes a fluid pump 112 and a pair of nozzles 114, 114′ that areconnected to reservoir 110. Fluid pump 112 can be located inside oroutside of reservoir 110 and nozzles 114, 114′ can extend into reservoir110 or can be routed outside of reservoir 110 to pump 112.

If desired, rather than directly pumping washer fluid to nozzles 114,114′ using fluid pump 112, an air-over-water system can be used in whichreservoir 112 is pressurized via a compressed air source (not shown) andsolenoid or other type of valve (not shown) is used to permitpressurized fluid from reservoir 110 through nozzles 114, 114′. Thecompressed air source can be an air pump that is used in lieu of washerfluid pump 112. The nozzles can be connected to a common supply line theextends directly into the interior of reservoir 112 via the valve.Alternatively, the nozzles can simply be tubes that extend directly intoreservoir 110. The electronic control system used to control motors 102,102′ can be coupled to a pressure sensor within reservoir 112 and can beused to control the supply of compressed air into the reservoir. Thecontrol system can also operate the valve to permit washing fluid tospray onto the windshield in response to activation by the vehicleoperator of a corresponding control switch. Moreover, the pressurewithin the reservoir can be controlled in accordance with variousoperational parameters to provide a controlled amount and rate of spray.For example, at highway speeds the air moving quickly over the surfaceof the vehicle often results in much of the washer spray missing thewindshield entirely and instead being carried over the roof of thevehicle. Therefore, at higher speeds the pressure within reservoir 112can be reduced so as to reduce the pressure and resulting atomization ofwasher fluid leaving the nozzles. For this purpose, an electronicallycontrolled valve can be used to selectively bleed air out of reservoir112 and this valve can also be controlled by the windshield wiperelectronic control system.

As can also be seen by reference to FIG. 8, drive shafts 106, 106′ andnozzles 114, 114′ both extend out through a cowl cover 116. This cowlcover can be an exterior trim piece that is separately connected to thevehicle such that the drive shafts and nozzles float within theirrespective apertures in the cowl cover. Alternatively, the cowl covercan be formed as a structural member that partially or entirely supportsreservoir 110 and/or motors 102, 102′.

Other variations will become apparent. For example, motors 102, 102′ andreservoir 110 could all be rigidly connected to a bracket that is usedto attach assembly 100 to the vehicle. Alternatively, reservoir 110could be rigidly mounted to the vehicle and could provide the necessarysupport for motors 102, 102′.

FIG. 9 depicts another embodiment of the mechanical assembly of theinvention in which the fluid reservoir 120 also forms the motor housingof one or both of the motors 122, 122′ (only one motor shown). In thisembodiment, the stator 124 is press fit into a cavity 120 a formed inthe outer surface of reservoir 120. An electrical connector 126 is usedto electrically connect the Hall effect sensors 127 and windings ofmotor 122 to the windshield wiper electronic control system 140. Therotor 128 extends out of motor 122 and into an integral gear box 130which has a drive shaft 132 that extends through cowl cover 134. Also,as shown in FIG. 9, reservoir 120 can also provide a mounting surface138 for control module 140. Also, in this embodiment, cowl cover 134forms the cover of reservoir 120 and can include nozzles as unitaryprojections from its outer surface. In this way, cowl cover 134 isutilized not only as exterior trim, but also as an integral part ofreservoir 120.

Reservoir 120 can be injection molded or, if appropriate, blow molded. Amotor housing formed from, for example, metal can be made an integralpart of reservoir 120 using insert molding or any other suitablemanufacturing process. Alternatively, a separate motor housing can bepress fit into cavity 120 a after reservoir 120 has been molded.Reservoir 120 can include tabs or other suitable fastening arrangementsfor retaining the motor housing within cavity 120 a.

Referring now to FIG. 10, an embodiment of the mechanical assembly isshown in which the washer fluid within the reservoir 150 is used as aheat sink for the heat generated by the power electronic devices 152(e.g., the power transistors used for commutation of the motorwindings). Reservoir 150 includes an integral bottom plate 154 and aplastic body 156 that are integrally joined about the perimeter of plate154. Plate 154 can be aluminum or other thermally conductive material.It can be joined to plastic body 156 during using an insert moldingprocess in which plate 154 is placed into the mold used to form body156. The power electronic devices 152 are fastened to an aluminum plate158 during assembly of the electronic control module. The power devicescan be thermally coupled to aluminum plate 158 via a thermal adhesive orusing fasteners and thermal grease between the power devices andaluminum plate. An electronic control module cover 160 can be used toenvironmentally isolate power devices 152 as well as other circuitcomponents. It will be appreciated that, if desired, the features of theembodiments of both FIGS. 9 and 10 could be incorporated into a singlewiper system.

If desired, the motors can also be thermally coupled to the washerfluid, e.g., by insert molding a metal motor housing as an integral partof the reservoir. In this regard, the shape of the reservoir may bedesigned so as to maximize the amount of heat transfer away from themotors and/or the power devices. The mechanical assembly can also bedesigned with the outlet(s) for the washer fluid (i.e., the inlets foreither the nozzles or washer fluid pumps) located at a certain distanceabove the bottom of the reservoir so that there will always be apreselected minimum amount of washer fluid available for removing heatfrom the power devices and/or motors.

Aluminum plate 158 and bottom plate 154 can be electrically grounded soas to ground the washer fluid within reservoir 150. This helps reducethe total EMI radiated by the electrical components of the windshieldwiper system. Also, the reservoir can be designed so as to substantiallyenclose some or all of the wiper system's electrical wiring to provideshielding from other radiated emissions.

The combination of independent motorized control of the wiper bladeswith use of the intervening space for an integrated reservoir and fluidspray system provides a single assembly that significantly simplifiesinstallation into the vehicle. The assembly is simply bolted to thevehicle and a single electrical plug can be used to connect the assemblyto the vehicle electrical system.

We claim:
 1. In a windshield wiper system for a vehicle, the wipersystem having a first electric motor, a second electric motor, a fluidreservoir, and a pump; said first electric motor being operable torotate a first drive shaft that is adapted to support a first wiperblade and said second electric motor being operable to rotate a seconddrive shaft that is adapted to support a second wiper blade, whereinsaid first motor and said first drive shaft are spaced from said secondmotor and second drive shaft by an intervening space; and said pumpbeing coupled to said reservoir to pump windshield wiper fluid from saidreservoir; characterized in that said motors, fluid reservoir, and pumpare connected together as a single assembly, wherein said assemblyincludes one or more mounting members that support said motors, fluidreservoir, and pump, and wherein said fluid reservoir is supported at afirst end by said first motor and is supported at said second end bysaid second motor, with said reservoir being constrained in saidintervening space between said motors.
 2. A windshield wiper system asdefined in claim 1, wherein said fluid reservoir includes first andsecond spaced recesses and wherein said first and second motors havehousings that extend into said first and second recesses, respectively.3. In a windshield wiper system for a vehicle, the wiper system having afirst electric motor, a second electric motor, a fluid reservoir, and apump; said first electric motor being operable to rotate a first driveshaft that is adapted to support a first wiper blade and said secondelectric motor being operable to rotate a second drive shaft that isadapted to support a second wiper blade, wherein said first motor andsaid first drive shaft are spaced from said second motor and seconddrive shaft by an intervening space; and said pump being coupled to saidreservoir to pump windshield wiper fluid from said reservoir;characterized in that said motors, fluid reservoir, and pump areconnected together as a single assembly, wherein said assembly includesone or more mounting members that support said motors, fluid reservoir,and pump, and wherein said fluid reservoir is supported at a first endby said first motor and is supported at said second end by said secondmotor, with said reservoir being constrained in said intervening spacebetween said motors; wherein said fluid reservoir includes first andsecond spaced recesses and wherein said first and second motors havehousings that extend into said first and second recesses, respectively;and wherein said fluid reservoir comprises a molded housing and whereinsaid first and second recesses are defined by respective first andsecond sets of fingers that extend from said molded housing.
 4. Awindshield wiper system as defined in claim 1, wherein said first andsecond motors are coupled to their associated drive shafts by respectivefirst and second gear boxes, wherein said one or more mounting memberscomprise a first mounting member secured to said first gear box and asecond mounting member secured to said second gear box.
 5. A windshieldwiper system as defined in claim 4, wherein said fluid reservoir extendsbetween and is supported by said first and second motors.
 6. In awindshield wiper system for a vehicle, the wiper system having a firstelectric motor, a second electric motor, a fluid reservoir, and a pump;said first electric motor being operable to rotate a first drive shaftthat is adapted to support a first wiper blade and said second electricmotor being operable to rotate a second drive shaft that is adapted tosupport a second wiper blade, wherein said fist motor and said firstdrive shaft are spaced from said second motor and second drive shaft byan intervening space; and said pump being coupled to said reservoir topump windshield wiper fluid from said reservoir; characterized in thatsaid motors, fluid reservoir, and pump are connected together as asingle assembly, wherein said assembly includes one or more mountingmembers that support said motors, fluid reservoir, and pump, and whereinsaid fluid reservoir includes first and second unitary portions thatcomprise housings for said first and second motors, respectively.
 7. Awindshield wiper system as defined in claim 6, wherein said first andsecond unitary portions define respective first and second recesses inan outre surface of said fluid reservoir.
 8. In a windshield wipersystem for a vehicle, the wiper system having a fist electric motor, asecond electric motor, a fluid reservoir, and a pump; said firstelectric motor being operable to rotate a first drive shaft that isadapted to support a first wiper blade and said second electric motorbeing operable to rotate a second drive shaft that is adapted to supporta second wiper blade, wherein said first motor and said first driveshaft are spaced from said second motor and second drive shaft by anintervening space; and said pump being coupled to said reservoir to pumpwindshield wiper fluid from said reservoir; characterized in that saidmotors, fluid reservoir, and pump are connected together as a singleassembly, wherein said assembly includes one or more mounting membersthat support said motors, fluid reservoir, and pump, and wherein saidfluid reservoir includes first and second unitary portions that comprisehousings for said first and second motors, respectively; and whereinsaid first and second motors each include a metal housing thermallycoupled to the interior of said fluid reservoir, whereby fluid withinsaid reservoir acts as a heat sink to thereby remove heat from saidmotors.
 9. In a windshield wiper system for a vehicle, the wiper systemhaving a first electric motor, a second electric motor, a fluidreservoir, and a pump; said first electric motor being operable torotate a first drive shaft that is adapted to support a first wiperblade and said second electric motor being operable to rotate a seconddrive shaft that is adapted to support a second wiper blade, whereinsaid first motor and said first drive shaft are spaced from said secondmotor and second drive shaft by an intervening space; and said pumpbeing coupled to said reservoir to pump windshield wiper fluid from saidreservoir; characterized in that said motors, fluid reservoir, and pumpare connected together as a single assembly, wherein said assemblyincludes one or more mounting members that support said motors, fluidreservoir, and pump, with said fluid reservoir being attached to saidone or more mounting members and wherein said fluid reservoir is locatedin said intervening space with said motors being supported thereof. 10.In a windshield wiper system for a vehicle, the wiper system having afirst electric motor, a second electric motor, a control circuit, afluid reservoir, and a pump; said first electric motor being operable torotate a first drive shaft that is adapted to support a first wiperblade and said second electric motor being operable to rotate a seconddrive shaft that is adapted to support a second wiper blade, whereinsaid first motor and said first drive shaft are spaced from said secondmotor and second drive shaft by an intervening space; and said pumpbeing coupled to said reservoir to pump windshield wiper fluid from saidreservoir; characterized in that said motors, fluid reservoir, and pumpare connected together as a single assembly, wherein said assemblyincludes one or more mounting members that support said motors, fluidreservoir, and pump, wherein said fluid reservoir includes at least onethermally conductive member that is thermally coupled to the interior ofsaid fluid reservoir, and wherein said control circuit includes one ormore power devices thermally coupled to said thermally conductivemember, whereby fluid within said reservoir acts as a heat sink tothereby remove heat from said one or more power devices via saidthermally conductive member.
 11. A windshield wiper system as defined inclaim 10, wherein said fluid reservoir comprises a molded housing havinga metal plate thermally coupled to the interior of said reservoir and tosaid one or more power devices.
 12. In a windshield wiper system for avehicle, the wiper system having a first electric motor, a secondelectric motor, a fluid reservoir, and a pump; said first electric motorbeing operable to rotate a first drive shaft that is adapted to supporta first wiper blade and said second electric motor being operable torotate a second drive shaft that is adapted to support a second wiperblade, wherein said fist motor and said first drive shaft are spacedfrom said second motor an second drive shaft by an intervening space;and said pump being coupled to said reservoir to pump windshield wiperfluid from said reservoir; characterized in that said motors, fluidreservoir, and pump are connected together as a single assembly, whereinsaid assembly includes one or more mounting members that support saidmotors, fluid reservoir, and pump, and wherein said fluid reservoirincludes a metal contact within a lower portion of the interior of saidreservoir, said contact being electrically grounded whereby windshieldwasher fluid within said reservoir is electrically grounded to therebyreduce electromagnetic interference radiated by said motors.
 13. In awindshield wiper system having a first motor, a second motor, and acontrol circuit having first and second outputs connected to said firstand second motors, respectively, said first and second motors eachincluding a brushless dc motor having an output shaft for providingrotation to an associated wiper blade and said first and second motorsfurther including an encoder that provides pulses indicative of angulardisplacements of the encoder's associated motor, wherein said controlcircuit is operable to use said pulses for commutation of said brushlessdc motors, characterized in that: said control circuit being furtheroperable to use said pulses to determine the position of at least one ofthe wiper blades, with said control circuit being operable to count atleast certain ones of said pulses and to determine the position of thewiper blade based upon said count.
 14. A windshield wiper system asdefined in claim 13, wherein said encoder utilizes Hall effect sensorsto generate said pulses.
 15. A windshield wiper system as defined inclaim 13, wherein said first and second motors each include a drivemodule that provides commutation of said motors using said pulses.
 16. Awindshield wiper system as defined in claim 13, wherein said controlcircuit provides commutation of said motors using said pulses.
 17. Awindshield wiper system as defined in claim 13, wherein, for each ofsaid motors, said control circuit is operable to track the position ofthe motor's associated wiper blade by incrementing a counter for eachpulse occurring as a result of rotation of the motor in one directionand decrementing the counter for each pulse occurring as a result ofrotation of the motor in the other direction.
 18. In a windshield wipersystem having a first motor, a second motor, and a control circuithaving first and second outputs connected to said first and secondmotors, respectively, said first and second motors each including anoutput shaft for providing rotation to an associated wiper blade and anencoder that provides pulses indicative of angular displacements of theencoder's associated motor, characterized in that said control circuitbeing operable to measure the magnitude of current flowing through atleast one of said motors and to determine a park position for the wiperblades using said measured current.
 19. In a windshield wiper systemhaving a first motor, a second motor, and a control circuit having firstand second outputs connected to said fist and second motors,respectively, said first and second motors each including an outputshaft for providing rotation to an associated wiper blade, and saidcontrol circuit being operable to control the position of the wiperblades, characterized in that said control circuit being operable todetermined a target position for each of the wiper blades based upondesired acceleration, velocity, and deceleration values.
 20. Awindshield wiper system as defined in claim 19, wherein said controlcircuit is operable to determine torque values for each motor based uponsaid acceleration, velocity, and deceleration values.
 21. A windshieldwiper system as defined in claim 20, wherein aid control circuit isoperable to determine said acceleration, velocity, and decelerationvalues in accordance with a user-selected wiper speed setting.
 22. Awindshield wiper system as define din claim 19, wherein said controlcircuit has an input for receiving a signal indicative of auser-selected wiper speed setting, and wherein said control circuit isoperable to minimize said acceleration and deceleration values whilepermitting the wiper blades to complete a wiping cycle in the timeallotted by the user-selected speed setting and while maintainingpositional synchronism between the wiper blades.
 23. In a windshieldwiper system having a first motor, a second motor, and a control circuithaving first and second outputs connected to said first and secondmotors, respectively, said first and second motors each including anoutput shaft for providing rotation to an associated wiper blade, andsaid control circuit being operable measure the current used by saidmotors, characterized in that said control circuit is operable todetermine an environmental condition of the windshield in accordancewith the measured current and is operable to change at least one of itsoutputs based upon said determined environmental condition.
 24. Awindshield wiper system as defined in claim 23, wherein said controlcircuit is operable to determine the environment condition using themeasured current and at least one other measured parameters.
 25. In awindshield wiper system having a first motor, a second motor, and acontrol circuit having first and second outputs connected to said firstand second motors, respectively, said first and second motors eachincluding an output shaft for providing rotation to an associated wiperblade, and said control circuit being operable measure the current usedby said motors, characterized in that said control circuit is operableto determine an environmental condition of the windshield in accordancewith the measure current and is operable to change at least one of itsoutputs based upon said determined environmental condition; wherein saidcontrol circuit is operable to determine the environment condition usingthe measured current and at least one other measured parameter; andwherein said other measured parameter is outside air temperature.
 26. Ina windshield washer system having a first motor, a second motor, a fluidreservoir, a pump, and a control circuit, said first and second motorseach including an output shaft for providing rotation to an associatedwiper blade, said control circuit being operable to control the spray ofwasher fluid onto the windshield, characterized in that said controlcircuit being operable to control the spray of washer fluid onto thewindshield in accordance with at least one measured parameter, whereinsaid control circuit is operable to track the position of the wiperblades and to spray washer fluid onto the windshield in synchronism withthe wiper blades.
 27. In a windshield wiper system having a first motor,a second motor, and a control circuit having first and second outputsconnected to said first and second motors, respectively, said first andsecond motors each including an output shaft for providing rotation toan associated wiper blade, wherein said motors are operable in anintermittent mode to reciprocate the wiper blades between an inboard andan outboard position, characterized in that said control circuit isoperable in an intermittent mode in which said control circuit operatesto pause said motors when the wiper blades reach both said inboard andoutboard positions.